out the following question, "Using the term circle as extending to the case where the radius is a pure imaginary, it is required to construct the common chord of two circles." This drew forth from Cayley a rejoinder in which he gave a solution of the problem. To which Airy replied, "I am not so deeply plunged in the mists of impossibles as to appreciate fully your explanation in this instance, or to think that it is a good criterion for University candidates." The dispute ended in the introduction of mathematical physics into the course of study.
Airy was a liberal in religious attitude. He sympathized with the agitation which led to the abolition of religious tests for M.A. degree at the Universities of Oxford and Cambridge. He also supported. his fellow mathematician Colenso when he was attacked for his writings on the Pentateuch. With respect to Colenso he wrote, "He has given me a power of tracing out truth to a certain extent which I never could have obtained without him. And for this I am very grateful. As to the further employment of this power he and I use it to totally different purposes. But not the less do I say that I owe to him a new intellectual power." During the years 1872-3 Airy was president of the Royal Society. In 1872 he was knighted by Queen Victoria; he had declined the honor three times before. In 1873 he was consulted by Barlow and Bouch the engineers for the construction of a railway bridge across the Firth of Tay, on the subject of the wind pressure that should be allowed for. This bridge was blown down in 1879 with a passenger train on it, no one surviving to tell the tale. Airy's report was subsequently much referred to at the official inquiry: into the causes of the disaster.
In 1881 when 80 years old (20 years over the limit assigned by Osler for good work!) Airy resigned the office of astronomer royal and the Government, on account of his exceptional public services, granted him a pension almost equal to his salary. He died on the 2d of January, 1892 in the 91st year of his age. His life had been one of great activity; he was the author of eleven volumes and of 518 papers extending from 1822 to 1887. With regard to his habits while he was at Green-
